Shree
Krishna Comments on the Hollow Earth

" You are fit in every way to perform the Rajasuya sacrifice and
become the world emperor, but you will first have to overthrow the
powerful Jarasandha, who has formed a near invincible alliance with
numerous other monarchs. He has extended his influence and control
throughout the middle portion of the earth and designs on the rest.
He is the biggest stumbling block to your plans."